Long-duration storage and the economics of battery investment

Robert Birdsey explains why long-duration storage has yet to achieve commercial viability, citing poor round-trip efficiency and weak market signals, while noting that short-duration storage benefits from wholesale price volatility and ancillary service revenues. Darpan Kapadia traces the evolution of battery storage from one-hour arbitrage projects to eight-hour systems that can deliver capacity value and transmission-like grid functions, arguing that up to eight hours of duration is now investable in the right markets.